Apparatus for use with a method for mass production of seedling of seed potato

ABSTRACT

A method of mass producing potato seedlings, involves collecting growing points of seed potatoes and culturing the growing points in a liquid or solid medium; introducing in vitro plantlets obtained from the culture of the growing points to solid culture; and removing the in vitro plantlets from the solid culture, and planting through stem cutting and acclimatizing the in vitro plantlets in deep flow culture, in which a nutrient solution is circulating. Upon planting in hydroponic facilities, such potato seedlings have high adaptability to the external environment and thus rapidly, uniformly generate roots in a short time. The rapid root anchoring prevents planted seedlings from withering, leading to death, growing poorly, and the like. The direct planting of in vitro plantlets through stem cutting without a separate acclimatization process shortens the overall production period of potato seedlings by omitting the acclimatization process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/552,265 filed Oct. 24, 2006 and based on and claims priority toKorean Patent Application Nos. 2005-100458 and 2005-103491 filed on Oct.24 and 31, 2005, respectively, as well as being related to anapplication entitled METHOD FOR MASS PRODUCTION OF SEEDLING OF SEEDPOTATO filed concurrently herewith, all of which are incorporated hereinby reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method of mass producing potatoseedlings, and more particularly to a method of mass producinghigh-quality disease-free potato seedlings, suitable for hydroponicgrowth, within a short period of time.

BACKGROUND

In the production of seed potatoes in hydroponics, it is most importantto produce disease-free potato seedlings, which are not infected withviruses and do not have seed-transmissible diseases, and to mass producehigh quality potato seedlings within a short period of time.

Once potato seedlings planted in culture beds for producing seedpotatoes become infected with viruses or develop major plant diseases,seed potatoes obtained from the infected seedlings are also infectedwith viruses or have major plant diseases through permanent seedtransmission, thereby losing their value as seed potatoes.

Thus, potato seedlings, which are used as starting materials in theproduction of disease-free seed potatoes, should be obtained fromvirus-free seedlings, which are propagated through in vitro tissueculture.

In addition, tissue-cultured seedlings, which are produced under cultureconditions of high humidity and low light levels, mostly wither and diewhen they are removed and immediately planted in the external airbecause the seedlings are grown in an in vitro-culture vessel, which hasa low flow of gas and energy and a small temperature change but has arelatively high humidity and a large diurnal change of CO₂concentration. The CO₂ concentration inside the closed culture vessel isabout 100 μmole·m-1, which is lower than 350 μmole/m·-2·s-1, during theday, but sharply increases to 3,000-9,000 μmole·m-1 in the dark. A largequantity of ethylene gas is generated in the vessel because the culturemedium is supplemented with sugars, salts and growth regulators and theculture vessel is completely closed to exclude external contaminants andthus prevent contamination. Also, since seedlings growing in the vesselhave low growth rates due to the high humidity inside the culture vesseland thus have morphology characterized by long internode lengths, thinstems and narrow leaves, they are not suitable for planting inhydroponics using a nutrient solution.

In vitro propagation through tissue culture, that is, solid culture,liquid culture or tank culture, incurs a high cost for seedlingproduction. This is because the mass production of geneticallyhomogenous seedlings generates completely functional individual plantsthrough culture under suitably sterile conditions, and thus is achievedwith facilities having expensive equipment and maintained under suitableconditions. Also, since the entire process is done manually and dependson experience, the labour cost accounts for about one half of theproduction cost. Also, plantlets grow slowly during propagation and areunable to adapt to the external environment during the acclimatizationprocess, resulting in low survival rates.

To be planted in greenhouse or other culture systems with a nutrientsolution, plantlets growing in culture bottles need to be stimulated togrow at the maximum rate and to grow into robust seedlings capable ofsurviving external stresses when exposed to the external environment.Thus, it is important in the production of potato seedlings to improvethe survival rates and quality of plantlets by suitably controlling theacclimatization of plantlets using an artificial method.

Potato seedlings may be produced by a method in which in vitro-culturedplantlets are acclimatized to become potato seedlings, which are thenplanted, or by another method in which minitubers weighing less than 5g, which are more difficult to provide for direct sowing in field of invitro-produced artificial seed potatoes or hydroponically grown seedpotatoes, are awoken from dormancy, allowed to sprout and grow to about7-8 cm in a sterile medium (perlite), and immediately planted asseedlings for planting in hydroponics after mother potatoes are removedtherefrom.

The acclimatization of in vitro-cultured plantlets to obtain potatoseedlings can be achieved using a method of producing seed potatoes,through on cutting and planting in vitro-culture acclimatized plantletsin sterile perlite culture to form new roots, or using a method ofproducing seed potatoes by acclimatizing in vitro-cultured plantlets indeep flow hydroponics to which a nutrient solution is supplied through apredetermined procedure and planting the acclimatized plantlets afterconducting stem cutting.

The production of potato seedlings through culture in perlite isachievable by allowing plantlets to grow in in vitro culture bottles ina greenhouse having the same environment as a culture room, in which thetemperature and light intensity are slowly increased, and air humidityis controlled by widening holes in the entrance. The in vitro-culturedplantlets thus acclimatized are removed from the culture bottles, rinsedwith pure water, and planted in a small-scale sterile perlite containerfor raising seedlings through cut planting or stem cutting to developnew roots on the stems, thereby functioning as seed potatoes. However,there is a very significant problem with this system, as follows. Whenthe planted potato seedlings are exposed to high air humidity orfrequent water supply during acclimatization, stems at regions of theplant that contact the perlite in order to develop new roots become verysoft and rot. Thus, rooted individuals are poorly acclimatized, and thusshow low survival. Also, since very high light levels cause stems towither, growers should suitably control the light intensity duringacclimatization according to the states of plantlets based on experienceand judgment. Moreover, the perlite used for acclimatization must bedisposed of due to contamination with pathogens, spreading of pathogens,excessive residual nutrients, and the like, and thus is a newenvironmental contaminant.

The soft rot and withering occur due to changes in growth environmentand the nature of in vitro-cultured plantlets. Since the in vitroculture system has a relative humidity of 90-100%, in vitro-grownplantlets have poor cuticle wax layers, and have smaller and fewerpalisade cells than common plants. Also, due to the high humidity, thestomata on leaves of the in vitro-grown plantlets always remain open,and thus are not functional. Roots and stems have poor vascularconnections, and thus in vitro-developed roots possess few or no roothairs. When solid medium-grown seedlings are removed from the in vitroconditions, roots extending into the medium are greatly damaged, and thein vitro-cultured seedlings thus cannot perform fully their originalfunction.

An alternative method of acclimatizing in vitro tissue-culturedplantlets into potato seedlings is based on manufacturing a culture bedusing a molded bed of Expanded polystylene and a plastic container box,planting cultured plantlets in an upper board of the culture bed coveredwith a black vinyl material to prevent internal leakage, and supplyingoxygen to a nutrient solution in a manner of supplying nutrients usingan air pump filled with the nutrient solution, thereby producing potatoseedlings. However, this method also has practical limitations in themass production of seed potatoes. Due to the nature of in vitro-culturedplantlets and changes in the growth environment, the cut regions of stemcuttings of potato plantlets rot, stems including growing points wither,and so on, thereby making the plantlets unable to grow. Since invitro-cultured plantlets utilize the limited nutrients contained in thenutrient solution, they lack specific growth nutrients. For a period ofabout 30 to 40 days required for the production of potato seedlings fromin vitro-cultured plantlets, seedlings shocked by nutrient deficiencymust be planted in hydroponic facilities after being diagnosed accordingto the expressed nutritional disorder symptoms and treated through thesupplement of deficient nutrients. However, to shorten theacclimatization and cultivation period, the shocked seedlings areimmediately planted in hydroponic facilities, causing growers greatloss. Also, since seedlings planted through stem cutting directly takeup nutrients contained in the culture bed, they are susceptible tocontamination by pathogens and to decay. In this case, all of thegrowing seedlings must be weeded out or discarded, wreaking havoc onpotato crops for that year.

Since technical skill and experience from failure lead to success in theproduction of potato seedlings from in vitro-cultured plantlets asdescribed above, beginning growers have difficulty in practice obtaininghigh quality potato seedlings. For this reason, in order to stablyobtain potato seedlings, seedling sprouts, which are obtained bybreaking the dormancy of seed potatoes having a predetermined size(minitubers) and sprouting the minitubers, are used. The seedlingsprouts are convenient for use as potato seedlings for planting due tothe following advantage. When minitubers having a size of lower than 5g, which are difficult to seed directly in field of in vitro-producedartificial seed potatoes and hydroponically grown seed potatoes, aredormancy broken, allowed to sprout and grow to about 7-8 cm in stemheight in a sterile medium (perlite), and immediately planted asseedlings for planting in hydroponics after mother potatoes are removedtherefrom, they can be immediately planted as young seedlings inhydroponics without the complicated acclimatization process required forin vitro-cultured plantlets.

However, there are drawbacks with the use of seedling sprouts. Sinceminitubers, like general potatoes, have various degrees of dormancy anddormancy periods according to the cultivar, they must be used afterconducting the cumbersome process of dormancy breaking. Also, whenseedling sprouts are generated using perlite and bed soil, they aresusceptible to viral contamination and other major diseases in seedpotatoes, leading to lower quality than initial tissuecultured-seedlings. Further, when minitubers to be used to generateseedling sprouts have poor or uncertified quality, they are unable to beused as potato seedlings.

It is also important to produce potato seedlings which are tall and havemany nodes on which stolons are formed in order to produce potatoseedlings suitable for hydroponics.

The cultivation method of producing seed potatoes by culturing potatoseedlings using a nutrient solution is based not on immersing potatoseedlings in the nutrient solution or culturing them in perlite or bedsoil, but on planting potato seedlings in the air by hanging them on ahollow Expanded polystylene culture bed. Since potato seedlings areinserted into slits formed on the side surface of a sponge in an up todown direction and pushed along with the sponge into planting holes onthe upper board of a culture bed. In the case of weak or over-grownpotato seedlings, even when growers with much planting experiencetransplant potato seedlings, even carefully, the planted seedlings areeasily broken and bent inside the sponge, eventually withering anddying. Further, since the planted seedlings do not wither due to watercontained therein although they are caught in the sponge, growers cannotfind such seedlings. When such seedlings wither, wilt or die due towater loss in the external environment as time goes, the growers findseedlings shocked by environmental stresses caused by planting states,and replant seedlings to replace the shocked seedlings with newseedlings. Thus, a lot of labor and many potato seedlings are requiredand wasted for replanting for a period ranging from the planting date tothe day on which a desired stand of seedlings is established. Also, dueto the uneven growth rates according to different rooting time for thegrowing potato seedlings and the newly planted potato seedlings,required nutrient concentrations and solution supply differ, and someseedlings display immature growth when converted to the reproductivegrowth period, resulting in low stolon generation. The resulting lowtuber formation reduces overall yields and prolongs growth periods,thereby imposing a burden on growers, to perform cultivation management,and causing related stress.

In addition, when produced potato seedlings are short, few or no stemnodes are exposed to the root zone below a culture bed due to thethickness of the upper board of the culture bed, which serves to supportpotato seedlings, and the thickness of the sponge into which seedlingsare inserted. Thus, planted seedlings have lower opportunity for rootingand stolon generation, resulting in decreased yields of seed potatoes.This is because the upper board of the compressed Expanded polystyleneculture bed through which planting holes are formed is about 5 cm thick,and the sponge into which the seedlings are planted in a state of beinginserted thereinto has the same thickness of 5 cm as the compressedExpanded polystylene culture bed, or is slightly thicker.

Thus, it becomes more important to produce seedlings having long stemsand many nodes, in which stolons, from which potatoes hang, aregenerated, the nodes exposed to the root zone below the culture bedexcept for the thickness of the sponge for planting. Such potatoseedlings may be produced by over-growing seedlings in a tender state ina dark room after being acclimatized, or by increasing the growth space.The former solution has the following problems. Seedlings have tenderstems due to low light levels and thus bend and fall over due to theirweight when grow past a certain level. Since such seedlings are easilybroken or bent inside the sponge when planted in facilities, they growpoorly or die, leading to low survival rates and poor seedlingestablishment. In the case of the latter, since the extended spaceenables sufficient photosynthesis, uniformly grown seedlings, which havean inverted triangular or diamond-shaped appearance of being short inplant height and having strong stems and short nodes, are obtained,thereby ensuring stable rooting. However, the latter method is alsoproblematic in that it does not guarantee a desired number of stolonsthrough the establishment of a sufficient number of nodes because thehydroponics method employs sponges. In contrast, when seedlings areover-grown and thus appear to have a high enough node number to be ableto form the maximal number of stolons, stems are hollow and angular, andthus change to nodes which are unable to form stolons from whichpotatoes will hang, and generate leaves and stems instead.

Therefore, there is an urgent need for the development of a method ofmass producing high quality potato seedlings suitable for the massproduction of seed potatoes in hydroponics.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a method of rapidly mass producing disease-freepotato seedlings having improved survival rates and rooting when plantedby preventing soft rot and rot in the root zone.

Another object of the present invention is to provide a method of massproducing seed potatoes using potato seedlings produced according to theabove method.

In order to accomplish the above objects, the present invention providesa method of mass producing potato seedlings, comprising a culturing stepof collecting growing points of seed potatoes and culturing the growingpoints in a liquid or solid medium; a solid culture step of introducingin vitro plantlets obtained from the culture of the growing points to asolid culture; and a deep-flow-stem-cutting-and-acclimatization (DSCA)step of removing the in vitro plantlets from the solid culture andplanting the in vitro plantlets through stem cutting and acclimatizingthem in deep flow culture in which a nutrient solution is circulating.

The present invention also provides a method of mass producing seedpotatoes, comprising planting the potato seedlings produced according tothe above method in hydroponic facilities; maximizing the number ofstolons by carrying out stem descending work for the planted potatoseedlings two or three times; and harvesting potato minitubers formed atthe stolons.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a photograph showing potato seedlings grown according to aconventional method using hydroponically grown seed potatoes, dormancyof which broken, and which are sown in perlite culture and allowed tosprout;

FIG. 2 is a photograph showing potato seedlings for planting inhydroponics, grown according to a conventional method, whereinartificial seed potatoes and hydroponically grown seed potatoes having asize of lower than 5 g are allowed to sprout and grow;

FIG. 3 is a photograph showing damage due to contamination upon tankculture among conventional methods of producing potato seedlings usingin vitro-cultured plantlets;

FIG. 4 is a photograph showing the development of soft rot in stemcuttings when in vitro-cultured plantlets are acclimatized and plantedthrough stem cutting to produce potato seedlings for planting inhydroponics according to a conventional method;

FIG. 5 is a photograph showing grafted and surviving potato seedlingswhen in vitro-cultured plantlets are acclimatized under externalconditions and planted through stem cutting in perlite culture accordingto a conventional method;

FIG. 6 is a photograph showing a short potato seedling which is insertedinto a planting sponge in hydroponic facilities for producing seedpotatoes according to a conventional method;

FIG. 7 is a photograph showing a potato seedling the stem of which isbroken when inserted into a planting sponge for planting in hydroponicfacilities for producing seed potatoes according to a conventionalmethod;

FIG. 8 is a photograph showing Superior potato seedlings produced usingin vitro-cultured plantlets according to the present invention, whereincuttings collected from the in vitro-cultured plantlets sprouted inDSCAC are replanted in SSCAC through stem cutting, and are subjected tostem descending work;

FIG. 9 is a photograph showing Superior potato seedlings grown inhydroponic facilities according to the present invention, wherein thepotato seedlings are produced using DSCAC and SSCAC according to thepresent invention and planted in hydroponic facilities;

FIG. 10 is a photograph showing in vitro plantlets grown from growingpoints of Superior potatoes according to the present invention, whereinthe growing points are grown in a basic MS medium of pH 5.8, which issupplemented with 80 g/L of sucrose and 9 g/L of agar, at 21° C. under4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrs for 25 days;

FIG. 11 is a photograph showing in vitro plantlets grown from growingpoints of Superior potatoes according to the present invention, whereinthe growing points are grown in a basic MS medium of pH 5.8, which issupplemented with 80 g/L of sucrose, 0.025 mg/L of coumarin and 9 g/L ofagar, at 21° C. under 4,500 Lux lighting for 18-20 hrs, and 0 Lux for4-6 hrs for 25 days;

FIG. 12 is a photograph showing in vitro plantlets grown from growingpoints of Superior potatoes according to the present invention, whereinthe growing points are grown in a basic MS medium of pH 5.8, which issupplemented with 2 g/L of hyponex, 80 g/L of sucrose and 9 g/L of agar,at 21° C. under 4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrsfor 25 days;

FIG. 13 is a photograph showing potato seedlings produced using invitro-cultured plantlets, wherein the plantlets are planted in DSCACthrough stem cutting and stimulated to generate terminal and lateralbuds under dark conditions according to the present invention;

FIG. 14 is a photograph showing potato seedlings, wherein sprouts(shoots) from the terminal and lateral buds generated in the dark arehardened by controlled radiation in which the light intensity isgradually increased according to the present invention;

FIG. 15 is a photograph showing potato seedlings produced using invitro-cultured plantlets, wherein the plantlets are planted in DSCACthrough stem cutting and are allowed to grow for 13 days according tothe present invention;

FIG. 16 is a photograph showing the large-scale collection of potatoseedlings grown in DSCAC according to the present invention and having asize of more than 5 cm to be used as potato seedlings for replantingthrough stem cutting;

FIG. 17 is a photograph showing potato seedlings for replanting throughstem cutting collected from DSCAC according to the present invention;

FIG. 18 is a photograph showing potato seedlings replanted in DSCACthrough stem cutting according to the present invention;

FIG. 19 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in DSCAC through stem cutting and then grown for 10 days,according to the present invention;

FIG. 20 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in DSCAC through stem cutting and then allowed to grow for 10days, according to the present invention;

FIG. 21 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in perlite culture through stem cutting and then grown for 10days according to the present invention;

FIG. 22 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in perlite culture through stem cutting and then grown for 15days, according to the present invention;

FIG. 23 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in perlite culture through stem cutting to be used as potatoseedlings for general soil culture, hardened, and grown for 10 days, andtransplanted into a plug tray filled with sterile bed soil and grown for10 days according to the present invention;

FIG. 24 is a photograph showing plug potato seedlings which are plantedin a greenhouse and grown for 25 days according to the present method;

FIG. 25 is a photograph showing potato seedlings for replanting throughstem cutting, which are collected from DSCAC, wherein the seedlings arereplanted in SSCAC through stem cutting and then grown for 10 daysaccording to the present invention;

FIG. 26 is a photograph showing potato seedlings which arestem-descended in SSCAC according to the present invention;

FIG. 27 is a photograph showing potato seedlings for planting inhydroponics, which are grown through DSCAC and SSCAC according to thepresent invention;

FIG. 28 is a photograph showing a potato seedling which has grownvigorously by taking up nutrients and water due to rapid rootdevelopment when cut to remove three quarters of the roots after beingproduced through SSCAC and planted in hydroponic facilities forproducing seed potatoes according to the present invention;

FIGS. 29 a and 29 b are photographs showing the tubers formed by theemergence of primary, secondary and tertiary stolons, on which potatoeshang up to the end of upper nodes of stems of seed potatoes when potatoseedlings produced according to the present invention are planted andcultivated in hydroponic facilities;

FIG. 30 illustrates the construction of DSCAC and SSCAC used forproducing potato seedlings according to the present invention;

FIG. 31 is a partial perspective view of a culture bed provided in asupport frame of DSCAC used for producing potato seedlings according tothe present invention;

FIG. 32 is a partial perspective view of a culture bed of DSCAC used forproducing potato seedlings according to the present invention;

FIG. 33 is a partial perspective view of a water discharge tube and anopening and closing tube, which are provided in a water outlet of aculture bed of DSCAC, which is used for producing potato seedlingsaccording to the present invention; and

FIG. 34 illustrates the operation of DSCAC and SSCAC, which are used forproducing potato seedlings according to the present invention.

DETAILED DESCRIPTION

Terms used herein are defined as follows.

The term “deep-flow-stem-cutting-and-acclimation (hereinafterabbreviated to as “DSCA”), as used herein, refers to a process ofplanting through stem cutting and cultivating tissue-cultured potatoseedlings in deep flow culture, in which a nutrient solution iscirculated.

The term “spraying-stem-cutting-and-acclimation” (hereinafterabbreviated to as “SSCA”), as used herein, refers to a process ofcultivating potato seedlings by spraying a nutrient solution to the rootzone of potato seedlings through nozzles.

The term “deep-flow-stem-cutting-and-acclimation-culture” (hereinafterabbreviated to as “DSCAC”), as used herein, refers to an apparatus inwhich the DSCA is performed.

The term “spraying-stem-cutting-and-acclimation-culture” (hereinafterabbreviated to as “SSCAC”), as used herein, refers to an apparatus inwhich the SSCA is performed.

The present invention provides a method of mass producing potatoseedlings, comprising a culturing step of collecting growing points ofseed potatoes and culturing the growing points in a liquid or solidmedium; a solid culture step of introducing in vitro plantlets obtainedfrom the culture of the growing points to a solid culture; and a DSCAstep of removing the in vitro plantlets from the solid culture andplanting through stem cutting and acclimatizing the in vitro plantletsin deep flow culture, in which a nutrient solution is circulated.

In the method of mass producing potato seedlings according to thepresent invention, the collected growing points may be cultured in asolid medium or a liquid medium. Liquid culture in a rotary shaker ispreferred.

The growing points of seed potatoes are preferably cultured for a periodranging from 24 to 26 days at 18-22° C. under 900-1,100 Lux lighting for18-20 hrs, and 0 Lux for 4-6 hrs in a basic MS medium of pH 5.7-5.8supplemented with 28-32 g/L of sucrose, or in such a medium furthersupplemented with 7-11 g/L of agar.

Preferably, the method further includes performing pathogen testing forthe in vitro plantlets after the growing points of seed potatoes arecultured. After the step of detecting viral infections or otherdiseases, potato seedlings identified as disease-free are selected andmass produced, thereby enabling the mass production of disease-freepotato seedlings, which are not infected with viruses or other diseases.Available disease identification methods are not specifically limited,but six species of viruses are preferably detected in each individualusing ELISA.

The solid culture is preferably composed of two sub-steps: primary shootsubculture and secondary propagation culture.

The primary shoot subculture is carried out preferably in a basic MSmedium of pH 5.7-5.8, which is supplemented with 7-11 g/L of agar and70-80 g/L of sucrose, and more preferably in a basic MS mediumsupplemented with 9 g/L of agar and 80 g/L of sucrose. The secondarypropagation culture is carried out preferably in a basic MS medium of pH5.7-5.8, which is supplemented with 7-11 g/L of agar, 70-80 g/L ofsucrose and 0.020-0.035 mg/L of coumarin, and more preferably in thebasic MS medium supplemented with 9 g/L of agar, 80 g/L of sucrose and0.025 mg/L of coumarin.

Since plant cells growing in vitro usually have lowered photosyntheticactivity, they should receive a carbon source from the culture medium inorder to get the energy required for cellular carbon skeletonmanufacture and metabolism. Taking into account the property of tissueculture undergoing a sterilization process (1.2 atm, 124° C.), sucrose,which is relatively stable at high temperatures, is preferred. Thesucrose added to the medium is taken up as an energy source for culturecells by plantlets, and thus affects cellular proliferation and growthas well as being involved in the redifferentiation of plantlets. Whensucrose is present in a large amount of 80 g/L, the best growth ofpotato seedlings is achieved.

In order to cultivate in vitro plantlets into potato seedlings havingrobust and elastic stems through exposure to the external dryenvironment, a large amount of carbohydrates should be accumulatedinside the plantlets even though light levels are low. For this, sucroseis most preferably used in an amount of 70-80 g/L. When sucrose ispresent in an amount lower than 70 g/L, no robust potato seedlings areobtained. When the amount of sucrose exceeds 80 g/L, reverse osmosisoccurs in the opposite direction of root pressure for nutrientabsorption, thus no carbohydrates are accumulated.

The primary shoot subculture and the secondary propagation culture areindividually carried out preferably for 25-35 days at 4,000-5,000 Lux,for 18-20 hrs, and 0 Lux for 4-6 hrs and more preferably for 30 days at4,500 Lux for 18-20 hrs, and 0 Lux for 4-6 hrs.

After the secondary propagation culture, the potato seedlings areremoved, and may be immediately subjected to DSCA, or subjected to DSCAafter being acclimatized. It is preferable to shorten the productionperiod so that the potato seedlings do not immediately undergo theacclimatization process but are immediately planted through stem cuttingin deep flow culture and then acclimatized.

Since tissue-cultured seedlings have been grown under in vitro closedconditions having high humidity and low light levels, they have lowgrowth rates, long internodes and thin stems. In order to betransplanted to a greenhouse or a hydroponics operation under dryconditions at high light levels, the tissue-cultured seedlings must beable to survive the stresses of the external environment. For this, theymust undergo an acclimatization process, in which the cultureenvironment of the in vitro plantlets is gradually changed to resemblethe external environment. However, the acclimatization process iscarried out for a long period ranging from about 10 to 15 days. Also, inspite of being acclimatized, in vitro plantlets have varying survivalrates according to the experience and ability of growers, and thedesired quality of seedlings may vary depending on growers. Therefore,as described in the present invention, it is very important to producepotato seedlings suitable in the external environment from in vitroplantlets for a shorter period through the DSCA step, without requiringa separate acclimatization process.

The potato seedlings planted in the DSCA step through stem cutting havestems from which all of the leaves have fallen. Preferably, the stemsare slightly old and thus are hardened. In the case in that potatoseedlings actively grown in vitro (for 30-35 days) are removed andplanted through stem cutting, since soft stems thick with leaves buthaving no roots are cut and planted, the leaves wither due tooverpropagation, and plantlets wilt and die, or have low rooting ratesdue to severe fatigue. When in vitro-cultured seedlings are removed in astate in which leaves are fallen and only stems remain and are thenplanted, 100% success is realized.

The potato seedlings to be planted in the DSCA step through stem cuttingare preferably cut at node regions at a lower part of stems with adisinfected sharp knife. Preferably, the seedlings are cut in only oneattempt. The DSCA step is preferably carried out with a nutrientsolution of pH 6.6-7.0 at a temperature of 18-22° C. Preferably, thelight intensity is gradually increased according to the growth phase inorder to gradually harden potato seedlings. Most preferably, the lightintensity is a) 0 Lux for 55-65 hours→b) 2,100 Lux for 45-55 hours, 0Lux for 4-8 hours→c) 3,600 Lux for 35-45 hours, 0 Lux for 4-8 hours→d)5,500 Lux for 25-35 hours, 0 Lux for 4-8 hours→e) 7,000 Lux for 535-545hours (lighting for 18-20 hours every day for 30 days), 0 Lux for120-180 hours (dark condition for 4-6 hours every day for 30 days).

After the stem cuttings have been planted, they are first incubatedunder dark conditions for a period of 55-65 hrs in order to generatewhite shoots. Since most plantlets take up nutrients dissolved in waterby the adhesion of water molecules resulting from transpiration throughground parts, the shoots primarily generated at terminal and lateralbuds stimulate the generation of root hairs, which are able to absorbnutrients and water into the planted root-zone stem cuttings. Thisensures the survival of in vitro-cultured plantlets with questionableviability. Also, when sprouts from the terminal and lateral buds ofplantlets are hardened by gradually increasing light levels from thedark condition, the plantlets have healthy dark-green leaves and a highaccumulation of carbohydrates, thereby having a good appearance, robustand not over-grown stems, and elastic and short nodes.

In the DSCA step, it is preferable that the supply of a nutrientsolution and the interruption of the nutrient solution supply berepeatedly alternated. Preferably, the nutrient solution is supplied for30-45 min, and the supply of the nutrient solution is then interruptedfor 90-180 min. This is because the frequent supply of the nutrientsolution leads to good growth of potato seedlings but brings about softrot due to excessive water uptake, and wilt occurs due to waterevaporation from seedlings when the nutrient solution is not suppliedfor a long period of time.

When the nutrient solution is supplied, it is preferable that thenutrient solution flow without fluctuation on the surface thereof and besupplied at a constant level. This is because rapid flow and swirling,which are caused by water pressure generated from the supplied nutrientsolution, stress potato seedlings planted through stem cutting, and thusinhibit rooting and growth.

When the supply of the nutrient solution is interrupted, it ispreferable that the supplied nutrient solution and growth debris becompletely discharged to expose stems and roots of potato seedlings tothe air. That is, the roots of potato seedlings are completely exposedto the air, and air influxes and circulates through holes for plantingof stem cuttings, which are formed in a culture panel, therebypreventing soft rot and root rot due to over-immersion and excessivewater uptake of potato seedlings planted through stem cutting.

In the DSCA step, it is preferable that potato seedlings be repeatedlycollected from 13-15 days after planting of stem cuttings at timeintervals of 6-10 days until nodes are exhausted. This results in alarge number of potato seedlings being obtained.

Preferably, the DSCA step is performed with a DSCAC, comprising aculture panel in which holes for planting stem cuttings are arranged toplant potato seedlings through stem cutting and cultivate the seedlings;a culture bed which has a space in which the culture panel is placed,contains a supplied nutrient solution required for the growth of thepotato seedlings planted through stem cutting in the culture panel, andhas a water outlet for discharging excess supplied nutrient solution; alight source which is provided at one side of the culture bed andradiates light on potato seedlings planted through stem cutting in theculture panel; a nutrient solution dispersion and supply tube which isprovided at one side of the culture bed and flows and supplies thenutrient solution to a lower part of the culture bed; and a nutrientsolution preparation and supply part which is equipped with a nutrientsolution tank, is connected to the nutrient solution dispersion andsupply tube and supplies the nutrient solution thereto.

In the DSCAC, the water outlet of the culture bed is provided with awater discharge tube having a slit in a longitudinal direction.Preferably, an opening and closing tube having a helical opening andclosing part is inserted into the water discharge tube in a separatedstate against the lower part of the water discharge tube.

In the DSCAC, the culture bed is formed in two layers by a support framein which the space in which the nutrient solution is held is formed intwo layers. The nutrient solution dispersion and supply tube connectedto the nutrient solution tube is placed in the space formed in eachlayer of the support frame. Fluorescent lamps as the light source arearranged in two rows in the lower part of the culture bed formed in eachlayer of the support frame. Herein, the nutrient solution dispersion andsupply tube in each layer is connected to one side of the support frameto supply the nutrient solution. A main supply tube having a flowcontrol valve for controlling the amount of inflowing nutrient solutionis placed between the nutrient solution dispersion and supply tubes. Themain supply tube is placed in an upright form such that it extends tothe upper part of the culture bed placed at the uppermost part of thesupport frame. The uppermost part of the main supply tube is larger involume than the lower part, and is coupled with a pressure tubeconnected to the nutrient solution tank. A pressure control valve forcontrolling the pressure against the main supply tube is placed betweenthe main supply tube and the pressure tube.

In the DSCAC, the water outlet of the culture bed preferably includes adischarge tube which is connected to the nutrient solution tank andrecovers the discharged nutrient solution into the nutrient solutiontank. Preferably, a micro-sieving net is placed at a terminal part ofthe discharge tube to sift sediments or impurities contained in thecirculating nutrient solution. This removal of sediments or impuritiesfrom the circulating nutrient solution prevents rot and soft rot at theroot zone.

In the DSCAC, one side of the nutrient solution dispersion and supplytube is a T-shaped branch tube into which the nutrient solution issupplied from the nutrient solution tank. The branch tube has aneffusion tube, in which a nozzle from which the nutrient solution flowsout is formed and which is horizontally provided at the lower surface ofthe culture bed in order to ensure stable flow of the nutrient solutionsupplied into the planted bed without fluctuation.

In the method of mass producing potato seedlings according to thepresent invention, the potato seedlings, having undergone the DSCA step,may be collected and replanted through stem cutting in any system,whether DSCAC, perlite culture, or SSCAC. Preferably, after the step ofdeep-flow-stem-cutting-and-acclimatization, the potato seedlings aresubjected to an SSCA step, in which a nutrient solution is sprayed ontothe root zone of the potato seedlings through nozzles.

The SSCA step is preferably performed in an SSCAC, comprising a culturepanel in which holes for planting stem cuttings are arranged to plantpotato seedlings through stem cutting and cultivate them; a culture bedin which the culture panel is supported at an upper part and which has aspray tube having nozzles spraying in a mist form a nutrient solutionrequired for the growth of the potato seedlings planted through stemcutting in the culture panel, and a water outlet for discharging thenutrient solution that has been sprayed and has flowed down; a lightsource which is provided at one side of the culture bed and radiateslight onto potato seedlings planted through stem cutting in the culturepanel; and a nutrient solution preparation and supply part which isequipped with a nutrient solution tank in which the spray tube of theculture bed is connected to one side and the nutrient solution isstored.

Preferably, the spray tube has a cleaning valve for dischargingsediments contained therein at a terminal part. The culture bed isformed in two layers by a support frame in which the space into whichthe nutrient solution is sprayed is formed in two layers. The spray tubeconnected to the nutrient solution tank is placed in the space providedin each layer of the support frame. Herein, the spray tube in each layeris connected to one side of the support frame to supply the nutrientsolution. A main supply tube having a flow control valve for controllingthe inflowing amount of the nutrient solution is placed between thespray tubes. The main supply tube is placed in an upright orientationsuch that it extends to an upper part of the culture bed placed at theuppermost part of the support frame. The uppermost part of the mainsupply tube is larger in volume than the lower part, and is coupled witha pressure tube connected to the nutrient solution tank.

Preferably, the water outlet of the culture bed includes a dischargetube which is connected to the nutrient solution tank and transfers thedischarged nutrient solution into the nutrient solution tank. Amicro-sieving net is placed at the terminal part of the discharge tubeto sift sediments or impurities introduced into the nutrient solutiontank.

The nutrient solution preparation and supply part preferably comprises astock solution tub which supplies a stock solution containing organicand inorganic nutrients to prepare the nutrient solution of the nutrientsolution tank; an acidic solution tub which is provided at one side ofthe stock solution tub and supplies an acidic solution to the nutrientsolution tank to control the acidity of nutrient solution tank; aquantization pump which is connected to the stock solution tub and theacidic solution tub, and receives the stock solution and the acidicsolution and supplies them to the nutrient solution tank inpredetermined amounts; a temperature control part, which controls thetemperature of the nutrient solution by receiving the nutrient solution,heating it and transferring it to the nutrient solution tank; a sensorpart, which is equipped with a nutrient solution temperature sensor formeasuring the temperature of the nutrient solution stored in thenutrient solution tank, a pH sensor for measuring acidity, and aconcentration sensor for measuring the nutrient concentrations of thenutrient solution; and a control part which controls the temperature ofthe nutrient solution by measuring the temperature of the nutrientsolution through the nutrient solution temperature sensor and operatingthe temperature control part, and controls the amount of the stocksolution and the acidic solution supplied to the nutrient solution tankthrough the quantization pump after checking the temperature,concentration and acidity of the nutrient solution through the pH sensorand the concentration sensor.

The nutrient solution preparation and supply part preferably includes awater level sensor which senses the water level in the nutrient solutiontank.

The nutrient solution tank of the nutrient solution preparation andsupply part is preferably equipped with a water disinfection part whichdisinfects the nutrient solution, and a bubble generation part whichgenerates bubbles in the nutrient solution.

Preferably, ultraviolet disinfection parts are placed in a tubeconnecting the nutrient solution tank and the culture beds in order todisinfect the nutrient solution.

The SSCA step is preferably performed with a nutrient solution of pH6.6-7.0 at 18-21° C. under 6,500-7,500 Lux for 18-20 hrs, and 0 Lux for4-6 hrs. The nutrient solution is preferably supplied for 30 sec andinterrupted for 4 min.

In the SSCA step, it is preferable that when the above-ground portion ofpotato seedlings has grown to about 8-12 cm in length, lower leavesexcept for two to four upper leaves be removed with disinfectedscissors, and stem descending work be carried out two or three times bydescending the stems of potato seedlings below the culture panel. Thiswork maximizes the number of round nodes from which stolons aregenerated, thereby maximizing the yield of seed potatoes.

Preferably, the SSCA step is performed during a period ranging from 32to 40 days, and all lower leaves except for two or three upper leavesare removed during the last 5-7 days. The roots of potato seedlings arecut to remove three quarters thereof, and are then allowed toregenerate. This process improves rooting rates in hydroponicfacilities.

Because, when potato seedlings are replanted through stem cuttingwithout the removal of developed roots, rooting occurs after the rootsof the potato seedlings planted through stem cutting have disappeared,it takes a longer time to generate new roots, the decay of the previousroots brings about stem soft rot and eventually plant death. When theroots of potato seedlings are completely removed, the leaves and stemswilt due to insufficient water uptake at the root zone, and thus, ittakes a longer time for seedlings to root, thereby making the initialgrowth of seedlings difficult. Thus, when the root regeneration isperformed after three quarters of the roots have been cut off, theplanted seedlings have improved rooting when planted in hydroponicfacilities.

Referring to the accompanying drawings, the construction and operationprinciple of the DSCAC and SSCAC, in which DSCA and SSCA are carriedout, will be described below.

FIG. 30 illustrates the construction of DSCAC and SSCAC, which are usedfor producing potato seedlings according to the present invention. FIG.31 is a partial perspective view of a culture bed provided in a supportframe of DSCAC, which is used for producing potato seedlings accordingto the present invention. FIG. 32 is a partial perspective view of aculture bed of DSCAC, which is used for producing potato seedlingsaccording to the present invention. FIG. 33 is a partial perspectiveview of a water discharge tube and an opening and closing tube, whichare provided in a water outlet of a culture bed of DSCAC, which is usedfor producing potato seedlings according to the present invention. FIG.34 illustrates the operation of DSCAC and SSCAC, which are used forproducing potato seedlings according to the present invention.

As illustrated in the drawings, the DSCAC according to the presentinvention comprises a culture panel 110 in which holes 101 for plantingstem cuttings are arranged to plant potato seedlings 105 through stemcutting and cultivate the potato seedlings 105; a culture bed 120 whichhas a space in which the culture panel 110 is placed, contains asupplied nutrient solution required for the growth of the potatoseedlings 105 planted through stem cutting in the culture panel 110, andhas a water outlet 111 for discharging excess supplied nutrientsolution; a light source 130 which is provided at one side of theculture bed 120 and radiates light onto potato seedlings 105 plantedthrough stem cutting in the culture panel 110; a nutrient solutiondispersion and supply tube 173 which is provided at one side of theculture bed 120 and flows and supplies the nutrient solution to thelower part of the culture bed 120; and a nutrient solution preparationand supply part 300 which is equipped with a nutrient solution tank 302,is connected to the nutrient solution dispersion and supply tube 173,and supplies the nutrient solution thereto.

After the potato seedlings 105 have been planted through stem cutting tothe culture panel 110, the culture panel 110 is supported by the upperpart of the culture bed 120. The roots of the potato seedlings 105planted in the culture panel 110 through stem cutting grow usingnutrients contained in the nutrient solution supplied to the culture bed120.

The water outlet 111 of the culture bed 120 is provided with a waterdischarge tube 115 having a slit 115 a in a longitudinal direction. Anopening and closing tube 116 having a helical opening and closing part116 a is inserted into the water discharge tube 115 in a separated stateagainst a lower part of the water discharge tube 115.

The water discharge tube 115 has a slit 115 a through which the nutrientsolution contained in the culture bed 120 is discharged. The opening andclosing tube 116 controls the water level of the nutrient solutioncontained in the culture bed 120 according to the length of the openedportion of the slit 115 a by controlling the length of the slit 115 a,which is connected to the water discharge tube 115, and is opened byrotation.

The opening and closing tube 116 is inserted into the water dischargetube 115 while the slit 115 a at the lower part of the water dischargetube 115 is opened, and controls the water level of the nutrientsolution according to the length of the opened portion of the slit 115 aby rotating an opening and closing part 116 a that has a singularstructure with the slit 115 a, or by rotating the slit 115 a to close.

The culture bed 120 is formed in two layers by a support frame 140 inwhich the space in which the nutrient solution is held is formed in twolayers. The nutrient solution dispersion and supply tube 173 connectedto the nutrient solution tube 302 is placed in the space formed in eachlayer of the support frame 140. Fluorescent lamps 131 as the lightsource are arranged in a double row in a lower part of the culture bed120 formed in each layer of the support frame 140.

Herein, the nutrient solution dispersion and supply tube 173 in eachlayer is connected to one side of the support frame 140 to supply thenutrient solution. A main supply tube 145 having a flow control valve142 for controlling the inflowing amount of the nutrient solution isplaced between the nutrient solution dispersion and supply tubes 173.The main supply tube 145 is placed in an upright orientation such thatit extends to the upper part of the culture bed 120 placed at theuppermost part of the support frame 140. The uppermost part of the mainsupply tube 145 is larger in volume than the lower part, and is coupledwith a pressure tube 150 connected to the nutrient solution tank 302. Apressure control valve 152 for controlling the pressure of the mainsupply tube 145 is placed between the main supply tube 145 and thepressure tube 150.

When the main supply tube 145 is fully filled with the nutrient solutionsupplied thereto, since the main supply tube 145 is in the uprightorientation, the main supply tube 145 applies spontaneous pressure tothe nutrient solution dispersion and supply tube 173 in proportion tothe height of the nutrient solution.

When the main supply tube 145 is overflowing with the nutrient solution,which flows in turn into the pressure tube 150, the nutrient solutionhas an increased flow rate when it passes through the pressure tube 150,thereby further increasing the pressure against a lower part of thepressure tube 150.

The pressure increase of the main supply tube 145 by the pressure tube150 is the result of the flow area at the lower part of the pressuretube 150 being narrower than at an upper part thereof. The increasedpressure in the main supply tube 145 due to the pressure tube 150 isapplied to the nutrient solution dispersion and supply tube 173connected to the upright main supply tube 145.

That is, the nutrient solution is supplied under a predeterminedpressure to the nutrient solution dispersion and supply tube 173connected to the upright main supply tube 145, flows along the bottomsurface of the culture bed 120, and is finally charged into the culturebed 120 to a predetermined height.

The height of the nutrient solution charged into the culture bed 120 isdetermined according to the extent of opening of the opening and closingtube 116 for the slit 115 a of the water discharge tube 115. Since theopening and closing tube 116 is coupled with the water discharge tube115 in a separated state against the lower part of the water dischargetube 115, the lower part of the slit 115 a of the water discharge tube115 is open, and the nutrient solution is discharged into the lower partof the slit 115 a of the opening and closing tube 116.

When the culture panel 110 plated with the potato seedlings 105 throughstem cutting is placed in the culture bed 120, the roots of the potatoseedlings 105 contact the nutrient solution, thereby being supplied withnutrients, and grow under the light supplied by the light source 130.The light source 130 radiates light on the potato seedlings 105 plantedthrough stem cutting, as follows: a) 0 Lux for 55-65 hours→b) 2,100 Luxfor 45-55 hours, 0 Lux for 4-8 hours→c) 3,600 Lux for 35-45 hours, 0 Luxfor 4-8 hours→d) 5,500 Lux for 25-35 hours, 0 Lux for 4-8 hours→e) 7,000Lux for 535-545 hours (lighting for 18-20 hours every day for 30 days),0 Lux for 120-180 hours (dark condition for 4-6 hours every day for 30days). The light levels emitted from the light source 130 are controlledby a timer 332.

The water outlet 111 of the culture bed 120 includes a discharge tube160 which is connected to the nutrient solution tank 302 and transfersthe discharged nutrient solution into the nutrient solution tank 302. Amicro-sieving net 162 is placed at the terminal end of the dischargetube 160 to filter out sediments or impurities contained in thecirculating nutrient solution.

The discharge tube 160 recovers the nutrient solution by transferring itinto the nutrient solution tank 302. The micro-sieving net 162 siftssediments or impurities contained in the nutrient solution recoveredafter being supplied to the potato seedlings 105, thereby enhancing thepurity of the nutrient solution to be supplied again to the culture bed120.

One side of the nutrient solution dispersion and supply tube 173 is aT-shaped branch tube 170 into which the nutrient solution is suppliedfrom the nutrient solution tank 302. The branch tube 170 has an effusiontube 172 in which nozzles 172 a from which the nutrient solution flowsout are formed, and which is horizontally provided at a lower surface ofthe culture bed 120. The branch tube 170 is connected to the main supplytube 145 and is supplied with the nutrient solution therefrom. Theeffusion tube 172 is formed in a transverse direction near the bottomsurface of the culture bed 120, and flows, in a longitudinal direction,the nutrient solution supplied from the branch tube 170 to the culturebed 120 through the nozzles 172 a.

Since the effusion tube 172 is formed in a transverse direction relativeto the culture bed 120 and thus evenly flows the nutrient solution in alongitudinal direction, the potato seedlings 105 uniformly grow andtheir growth is not hindered by the flow pressure of the nutrientsolution.

An SSCAC, which is provided at one side of a DSCAC, comprises a culturepanel 205 in which holes 201 for planting of stem cuttings are arrangedto plant potato seedlings 106 through stem cutting and cultivate them; aculture bed 222 in an upper part of which the culture panel 205 issupported and which has a spray tube 210 having nozzles 211 spraying ina mist form a nutrient solution required for the growth of the potatoseedlings 106 planted through stem cutting in the culture panel 205, anda water outlet 215 for discharging the nutrient solution that has beensprayed and has flowed down; a light source 230 which is provided at oneside of the culture bed and radiates light on the potato seedlings 106planted through stem cutting in the culture panel 205; and a nutrientsolution preparation and supply part 300 which is equipped with anutrient solution tank 302, to one side of which the spray tube 210 ofthe culture bed 222 is connected, and in which the nutrient solution isstored.

The spray tube 210 has a cleaning valve 212 at a terminal part todischarge sediments contained therein when the spray tube 210 is opened.When the nutrient solution in the nutrient solution tank 302 is suppliedto the spray tube 210 after the cleaning valve 212 has been opened, thenutrient solution that has flowed out from the nutrient solution tank302 discharges sediments accumulated inside the spray tube 210.

The culture bed 222 is formed in two layers by a support frame 240 inwhich the space into which the nutrient solution is sprayed is formed intwo layers. The spray tube 210 connected to the nutrient solution tank302 is placed in the space provided at each layer of the support frame240, and sprays the nutrient solution from the nutrient solution tank302 in a mist form.

The spray tube 210 has nozzles 211 for spraying the nutrient solution ina mist form, and is placed at the lower part of the culture bed 222 in alongitudinal direction.

The light source is controlled by a timer 332 to supply the light levelsrequired according to the growth phases of the potato seedlings 106planted in the culture bed 222 through stem cutting.

The spray tube 210 in each layer is connected to one side of the supportframe 240 to supply the nutrient solution. A main supply tube 245 havinga flow control valve for controlling the inflowing amount of thenutrient solution is placed between the spray tubes 210. The main supplytube 245 is placed in an upright orientation such that it extends to theupper part of the culture bed 222 placed at the uppermost part of thesupport frame 240. The uppermost part of the main supply tube 245 has anarrower flow area than the lower part, thereby increasing the pressurein the main supply tube 245 connected to the lower part thereof, andcoupled with a pressure tube 250 connected to the nutrient solution tank302. A pressure control valve 252 is placed at a lower position in thepressure tube 250, and controls the pressure against the main supplytube 245 by controlling the flow levels of the nutrient solution for thepressure tube 250.

Since the pressure tube 250 has a lower flow area than the main supplytube 245, the nutrient solution has an increased flow rate when itpasses through the pressure tube 250, and the main supply tube 245connected to the lower part of the pressure tube 250 maintains higherpressure than the pressure tube 250. This high pressure is applied tothe nutrient solution to efflux into the spray tube 210. Since apressure control valve 252 is formed between the pressure tube 250 andthe main supply tube 245 to control the level of flow of the nutrientsolution into the pressure tube 250, the pressure of the main supplytube 245 is controlled by controlling the flow levels of the nutrientsolution to be recovered in the nutrient solution tank 302 using thepressure control valve 252.

The water outlet 215 of the culture bed 222 includes a discharge tube260 which is connected to the nutrient solution tank 302 and recoversthe discharged nutrient solution into the nutrient solution tank 302. Amicro-sieving net 262 is placed at a terminal part of the discharge tube260 to sift sediments or impurities introduced into the nutrientsolution tank 302.

The DSCAC and SSCAC are installed in the same indoor space. In order tocultivate the potato seedlings 105, which are obtained by in vitroculturing growing points collected from a seed potato cultivar that hasbeen ascertained to be virus-free, into potato seedlings 106 suitablefor use in hydroponic facilities to obtain seed potatoes, the potatoseedlings 105 should be grown to a predetermined length in the culturebed 120 containing the nutrient solution. Then, the potato seedlings106, which are obtained by cutting an upper part of the potato seedlings105 to a predetermined length, should be planted through stem cutting inthe culture panel 205 of another culture bed 222 in which the nutrientsolution is sprayed in a mist form, and grown to a predetermined length.

The DSCAC and SSCAC are provided in such a way that the nutrientsolution tank 302 of the nutrient solution preparation and supply part300 is sandwiched between them, and supplied with the nutrient solutionthrough the operation of nutrient solution supply pumps 361 and 362,which are provided on both sides of the nutrient solution tank 302.

The nutrient solution preparation and supply part 300 comprises a stocksolution tub 305 which supplies a stock solution containing organic andinorganic nutrients to prepare the nutrient solution of the nutrientsolution tank 302; an acidic solution tub 307 which is provided on oneside of the stock solution tub and supplies an acidic solution to thenutrient solution tank 302 to control the acidity of the nutrientsolution tank; and a quantization pump 310 which is connected to thestock solution tub 305 and the acidic solution tub 307, and receives thestock solution and the acidic solution and supplies them to the nutrientsolution tank 302 in predetermined amounts.

The nutrient solution preparation and supply part 300 further comprisesa temperature control part 312 which controls the temperature of thenutrient solution by receiving the nutrient solution, heating it andtransferring it to the nutrient solution tank 302; and a sensor part 320which is equipped with a nutrient solution temperature sensor 315 formeasuring the temperature of the nutrient solution stored in thenutrient solution tank 302, a pH sensor 316 for measuring the aciditythereof, and a concentration sensor 317 for measuring the nutrientconcentrations of the nutrient solution.

The nutrient solution preparation and supply part 300 further comprisesa control part 340 which controls the temperature of the nutrientsolution by measuring the temperature of the nutrient solution using thenutrient solution temperature sensor 315 and operating the temperaturecontrol part 312, and controls the amount of the stock solution and theacidic solution supplied to the nutrient solution tank 302 through thequantization pump 310 by checking the temperature, concentration andacidity of the nutrient solution using the pH sensor 316 and theconcentration sensor 317.

The nutrient solution preparation and supply part 300 includes a waterlevel sensor 342 which senses the water level of the nutrient solutiontank 302. The nutrient solution tank 302 of the nutrient solutionpreparation and supply part 300 is equipped with a water disinfectionpart 345 which disinfects the nutrient solution, and a bubble generationpart 348 which generates bubbles in the nutrient solution.

Ultraviolet disinfection parts 346 and 347 are placed in a tubeconnecting the nutrient solution tank 302 and the culture beds 120 and222 in order to disinfect the nutrient solution.

Referring to FIG. 34, a process for supplying the nutrient solutionprepared by the nutrient solution preparation and supply part 300 to thepotato seedlings 105 and 106 of the culture beds 120 and 222 will bedescribed below.

First, when the quantization pump 310 is operated, the stock nutrientsolution in the stock solution tub 305 and the acidic solution in theacidic solution tub 307 are supplied to the nutrient solution tank 302,and raw water is supplied to the nutrient solution tank 302 through araw water tube 303.

The control part 340 senses the acidity and concentration of thenutrient solution through the pH sensor 316 and the concentration sensor317 provided in the nutrient solution tank 302, and controls thequantization pump 310 in order to control the amount of the stocksolution and the acidic solution, which are supplied through thequantization pump 310, thereby adjusting the acidity and concentrationof the nutrient solution prepared in the nutrient solution tank 302 tolevels appropriate for the growth of the potato seedlings 105 and 106.

The control part 340 senses the temperature of the nutrient solutionusing the temperature sensor 315 provided in the nutrient solution tank302, and circulates the nutrient solution into the temperature controlpart 312, thereby adjusting the temperature of the nutrient solution tothe temperature required for the growth of the potato seedlings 105 and106.

The nutrient solution is disinfected by operating the water disinfectionpart 345 provided inside the nutrient solution tank 302. The bubblegeneration part 348 generates bubbles to supply oxygen to the nutrientsolution.

When the nutrient solution supply pump 361 provided in a lateral part ofthe nutrient solution tank 302 is operated, the nutrient solution issupplied to the culture bed 120 provided in the nutrient solutiondispersion and supply tube 173. The nutrient solution is disinfectedwith ultraviolet radiation once more when it passes through theultraviolet disinfection part 346 provided in the lower part of the mainsupply tube 145.

The main supply tube 145 is filled with the supplied nutrient solution.When the main supply tube 145 is filled with the nutrient solution up tothe pressure tube 150 provided at an upper part thereof, the flowcontrol valve 142 between the nutrient solution dispersion and supplytube 173 and the main supply tube 145 is opened in order to supply thenutrient solution to the branch tube 170 of the nutrient solutiondispersion and supply tube 173 and flow the nutrient solution to thelower part of the culture bed 120 through the effusion tube 172 of thebranch tube 170.

The nutrient solution is contained in the culture bed 120 up to apredetermined water level. Nutrient solution above the predeterminedwater level is recovered to the nutrient solution tank 302 through theslit 115 a of the water discharge tube 115, which is provided in thewater outlet 111 of the culture bed 120.

That is, the length to which the slit 115 a of the water discharge tube115 is opened is controlled by the opening and closing tube 116. Thenutrient solution effluxes through a predetermined part of the openedslit 115 a. The opening and closing part 116 a provided in the openingand closing tube 116 is formed in a helical form to allow the slowinflux of the nutrient solution from a lateral direction, therebypreventing the roots of the potato seedlings 105 planted in the culturepanel 110 through stem cutting from being affected by the flow of thedischarged nutrient solution.

The slit 115 a at the lower part of the water discharge tube 115 isalways opened because the opening and closing tube 116 is inserted intothe water discharge tube 115 in a separated state against the lower partof the water discharge tube 115. When the operation of the nutrientsolution supply pump 361 is stopped to interrupt the supply of thenutrient solution from the nutrient solution dispersion and supply tube173, the nutrient solution is discharged through the lower opening ofthe slit 115 a.

When the supply of the nutrient solution from the nutrient solutiondispersion and supply tube 173 is interrupted, the nutrient solution isdischarged, and thus, the supply of the nutrient solution to the rootsof the potato seedlings 105 is interrupted. The roots of the potatoseedlings 105 are dried in the air, thereby preventing root rot or stemsoft rot, which usually occurs when the nutrient solution iscontinuously contained in the culture bed 120.

The nutrient solution discharged through the water outlet 111 of theculture bed 120 flows again into the nutrient solution tank 302 throughthe discharge tube 160. The micro-sieving net provided at the terminalend of the discharge tube 160 filters out sediments or impuritiescontained in the nutrient solution, thereby preventing the re-suppliednutrient solution from being contaminated with the sediments orimpurities.

When the nutrient solution in the nutrient solution tank 302 is suppliedto the culture bed 120, the light source 130 is operated to radiatelight onto the potato seedlings planted in the culture panel 110 throughstem cutting, as follows: a) 0 Lux for 55-65 hours→b) 2,100 Lux for45-55 hours, 0 Lux for 4-8 hours→c) 3,600 Lux for 35-45 hours, 0 Lux for4-8 hours→d) 5,500 Lux for 25-35 hours, 0 Lux for 4-8 hours→e) 7,000 Luxfor 535-545 hours (lighting for 18-20 hours every day for 30 days), 0Lux for 120-180 hours (dark condition for 4-6 hours every day for 30days).

The light source 130 includes four fluorescent lamps placed in the lowerpart of the culture bed 120. The time for which light is supplied by thefluorescent lamps 131 is controlled by a timer 332. The timer 332controls light levels by regulating the number of illuminatedfluorescent lamps 131 and the time that each fluorescent lamp isilluminated.

When the potato seedlings 105 grow to a predetermined length in theculture bed 120, workers cut the potato seedlings 105 to a predeterminedlength. The stem cuttings are planted and grown in the culture bed 222provided at the opposite side of the nutrient solution tank 302. Thisensures multiple node formation and stem hardness in the roots of thepotato seedlings 105, thereby growing the potato seedlings into potatoseedlings suitable for producing seed potatoes in hydroponic facilities.

That is, the stem cuttings of the potato seedlings 106 from the culturebed 120 provided on the right side of the nutrient solution tank 302 areplanted in the culture panel 205 of the culture bed 222 provided on theleft side of the nutrient solution tank 302. When the nutrient solutionsupply pump 362 provided on the left side of the nutrient solution tank302 is operated, the nutrient solution is disinfected through theultraviolet disinfection part 347 provided at the main supply tube 245,and supplied to the spray tube 210 provided over the culture bed 222.The nozzles formed in a row in the spray tube 210 spray the nutrientsolution in a mist form. The sprayed nutrient solution bounces off ofboth inner wall surfaces of the culture bed 222 and is then sprayed,thereby being supplied to the root zone of the potato seedlings 106.

After the nutrient solution is supplied to the potato seedlings, itflows down to the lower part of the culture bed 222, and is recovered inthe nutrient solution tank 302 through the water outlet 215. Thedischarge tube 260 recovering the nutrient solution has themicro-sieving net 262 at a terminal part thereof in order to siftsediments and impurities from the recovered nutrient solution.

When the light source 230 provided at the lower part of the culture bed222 is turned on, the fluorescent lamps 235 comprising the light source230 are operated. The fluorescent lamps 235 are controlled by the timer332, thus the potato seedlings 106 grow into potato seedlings suitablefor planting in hydroponic facilities.

In addition, the present invention provides a method of mass producingseed potatoes, comprising planting the potato seedlings producedaccording to the above method in hydroponic facilities; maximizing thenumber of stolons by carrying out stem descending work for the plantedpotato seedlings two or three times; and harvesting potato minitubersformed at the stolons. For the mass production of seed potatoes, thepotato seedlings planted in hydroponic facilities preferably have alength of 30-40 cm. The inside of hydroponic facilities is preferablymaintained at 18-21° C. The light levels, which are measured during theday time from twelve to one o'clock, are preferably 80,000-100,000 Luxon clear days, 25,000-35,000 Lux on cloudy days, and 10,000 Lux on rainydays. The nutrient solution used has a pH value from 6.6 to 7.0.Preferably, the nutrient solution is supplied for 30 sec, and supplythereof is then interrupted for 4 min.

A better understanding of the present invention may be obtained throughthe following examples which are set forth to illustrate, but are not tobe construed as the limit of the present invention.

EXAMPLE 1 Production of Potato Seedlings

1. Collection of Growing Points from Seed Potatoes and Liquid Culture

Disease-free seed potatoes were selected from a known potato cultivar.They were grown under semi-shaded diffused light until potato eyes(sprouts) thereof were about 0.5 cm, or were potted in sterile perliteabout two times as deep as the size of the potatoes. Herein, the seedpotatoes were isolated from contaminants, including insect vectors suchas mites, using a 540 mesh.

One node at an upper part of the stem of the illuminated seed potatoes,which has growing points of eyes or sprouts, was treated with one or twodrops of Tween-20 as a surfactant, sufficiently rinsed with runningwater, placed into a container having a lid, and transferred to a cleanbench.

The rinsed node was surface-disinfected with 70-75% ethanol for 30 sec,and rinsed with sterile water two or three times. The node wassurface-disinfected with 2% hypochlorite for 5-10 min, and rinsed withsterile water two or three times. After the node was transferred to aschale, a growing point was collected in a size of 0.2-0.3 mm (havingabout two primordial leaves) under a microscope. The collected growingpoints were planted in a liquid medium of pH 5.8, which was preparedwith an MS basic medium and 30 g/L sucrose, and incubated for 25 days ina rotary shaker at 80 rpm.

2. Pathogen Testing for In Vitro Tissue-Cultured Plantlets Using ELISA

Since a large number of individuals should be obtained for pathogentesting of in vitro plantlets grown in the liquid medium, the in vitroplantlets were propagated about four times in 500-ml culture bottlescontaining 200 ml of a solid medium.

After each plantlet was labeled for identification, a test sample wascollected. Juices were extracted from eighteen subcultured seedlings inthe same parental line. An antibody was diluted 1,000 times with astandard coating buffer (20 μl antibody in 20 ml buffer), and 200 μl ofthe antibody dilution were added to each well of a 96-well plate. The96-well plate was incubated in a humid container at 30° C. for 4 hrs.The 96-well plate was then washed with washing buffer four to eighttimes, and all of the water was removed from the plate. Each juice wasdiluted to a 1:10 or 1:20 ratio with extraction buffer, and 200 μl ofthis dilution was added to each well. The 96-well plate was incubated inthe humid container at 4° C. for 16 hrs (overnight). The 96-well platewas washed with washing buffer four to eight times, and water wascompletely removed from the plate. Conjugate IgG was diluted to 1,000times with conjugate buffer, and 200 μl of this dilution was added toeach well. The 96-well plate was incubated in the humid container at 30°C. for 5 hrs. The 96-well plate was then washed with washing buffer fourto eight times. One substrate pill was dissolved in 20 ml of substratebuffer, and 200 μl of this dilution was added to each well. The 96-wellplate was incubated under a dark condition at room temperature for 1 hr.Absorbance was measured at 405 nm using a microplate reader (Bio-Rad,Model 550).

3. Subculture and Propagation of Pathogen-Tested In Vitro Plantlets

The pathogen-tested in vitro plantlets were planted in 500-ml culturebottles containing 200 ml of a solid medium, which was prepared with abasic MS medium of pH 5.8 supplemented with 70-80 g/L of sucrose and 9g/L of agar. The plantlets were then allowed to grow in a culture roomunder 4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrs for 30days, the room temperature being maintained at 21° C. using an airconditioner.

Then, the plantlets were planted in 500-ml culture bottles containing200 ml of a solid medium, which was prepared with a basic MS mediumhaving a pH of 5.8 supplemented with 9 g/L of agar, 80 g/L of sucroseand 0.025 mg/L of coumarin. The plantlets were incubated until theleaves had fallen off and only stems remained, in a culture room under4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrs using 4Dfluorescent lamps, wherein the room temperature was maintained at 21° C.using an air conditioner.

4. DSCA of Potato Seedlings

The propagated potato seedlings were planted through stem cutting andcultivated in a DSCAC, which was prepared using a square aluminum tubehaving a size of 4 cm. The DSCAC had a three layer structure of 132 cmlong×60 cm wide×230 cm high, in which each layer was 45 cm high.

After the potato seedlings were removed from the culture bottles, noderegions at lower parts of stems were cut out using a disinfected sharpknife. The cuttings were planted in holes for planting stem cuttings inDSCAC. The indoor temperature was maintained at 18° C. The radiationstarted from 0 Lux for 60 hrs, and the light intensity was graduallyincreased to 2,100 Lux for 45-55 hours, 0 Lux for 4-8 hours→3,600 Luxfor 35-45 hours, 0 Lux for 4-8 hours→5,500 Lux for 25-35 hours, 0 Luxfor 4-8 hours→7,000 Lux for 535-545 hours (lighting for 18-20 hoursevery day for 30 days), 0 Lux for 120-180 hours (dark condition for 4-6hours every day for 30 days), thereby hardening the stem cuttings. Anutrient solution having a pH of 6.8 was used. The nutrient solution wassupplied for 30 min, and the supply thereof was interrupted for 120 min.Potato seedlings were repeatedly collected 13-15 days after planting ofstem cuttings at time intervals of 6-10 days until nodes were exhausted.

5. SSCA of Potato Seedlings

The potato seedlings, having undergonedeep-flow-stem-cutting-and-acclimatization, were planted through stemcutting in a SSCAC, which was prepared using a square aluminum tubehaving a size of 4 cm. The SSCAC had a three layer structure 260 cmlong×60 cm wide×230 cm high, in which each layer was 60 cm high. TheSSCA was carried out using a nutrient solution of pH 6.8 under 7,000 Luxlighting for 18-20 hrs, and 0 Lux for 4-6 hrs at 21° C. The nutrientsolution was supplied to the potato seedlings in the form ofmicroparticles (mist particles) through spray nozzles. The nutrientsolution sprayed onto the potato seedlings was supplied for 30 sec, andthe supply of the nutrient solution was interrupted for 4 min. Thesupply and interruption thereof of the nutrient solution were repeatedlyalternated. When the above-ground portion of potato seedlings had grownto about 10 cm in length, lower leaves, other than the three uppermostleaves, were removed with disinfected scissors, and stem descending workwas carried out three times by descending the stems of potato seedlingsbelow the culture panel. All of the lower leaves, but not the threeuppermost leaves, were removed during the last 5-7 days of SSCA. Theroots of potato seedlings were cut to remove three quarters thereof, andthen allowed to regenerate.

EXAMPLE 2 Production of Seed Potatoes

The potato seedlings having a plant length of 35 cm, prepared in Example1, were planted in hydroponic facilities. The potato seedlings werecultivated at 21° C. using a nutrient solution of pH 6.8. The nutrientsolution sprayed onto the potato seedlings was supplied for 30 sec, andthe supply of the nutrient solution was interrupted for 4 min. Thesupply and interruption thereof of the nutrient solution were repeatedlyalternated. When the above-ground portion of the potato seedlings hadgrown to about 10 cm in length, the lower leaves, but not the threeuppermost leaves, were removed with disinfected scissors, and stemdescending work was carried out three times by descending the stems ofpotato seedlings below the culture panel. Thereafter, potato minituberswere repeatedly collected.

TEST EXAMPLES 1 TO 3

In order to determine conditions suitable for planting through stemcutting and acclimatizing tissue-cultured plantlets in DSCAC, the invitro potato seedlings were evaluated for seedling quality and survivalrates upon stem-cutting and acclimation according to the amount ofsupplemented components of MS medium.

The culture seedlings obtained from growing points collected from a seedpotato cultivar, were tested for infection with viruses (PLRV, PVY, PVX,PVM, PVS and AMV) for selection of disease-free individuals. Then,plantlets were planted in 500-ml culture bottles containing 200 ml of asolid medium, which was prepared with a basic MS medium of pH 5.8supplemented with 9 g/L of agar, and incubated for 25 days in a cultureroom under 4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrs using4D fluorescent lamps, wherein the room temperature was maintained at 21°C. using an air conditioner. The in vitro potato seedlings were examinedfor growth states and survival rates upon stem-cutting and acclimationaccording to the amount of supplemented components of the medium. Aknown potato cultivar, “Superior”, was used in this test.

The results are given in Tables 1 to 3, below.

TABLE 1 Sucrose (g/L) 0 20 40 60 80 100 120 140 Plant length 5.0 6.2 7.49.3 9.5 6.1 5.2 2.1 (cm/plant) Fresh weight 0.45 0.47 0.53 0.58 0.750.69 0.63 0.67 (cm/plant) Survival rates 13% 27% 34% 59% 71% 68% 67% 72%of stem cuttings

Table 1 shows the seedling quality and survival rates of the in vitrotissue-cultured plantlets according to the amount of sucrose added tothe MS medium as an energy source. As shown in Table 1, sucrose was mostbeneficial to the in vitro plantlets when used in an amount of 80 g/L,as indicated by plant length, fresh weight and survival rates of stemcuttings.

TABLE 2 Coumarin (mg/L) 0 0.010 0.015 0.020 0.025 0.030 0.035 Sucrose(g/L) 30 80 30 80 30 80 30 80 30 80 30 80 30 80 Plant 5.3 8.6 6.1 7.86.5 7.9 6.7 8.1 6.9 9.5 6.7 8.3 6.4 8.2 length (cm/plant) Fresh 0.530.72 0.57 1.12 0.63 1.13 0.71 1.31 0.84 1.65 0.86 1.39 0.71 1.36 weight(cm/plant) Survival 33 70 73 90 78 92 80 100 83 100 88 100 81 100 ratesof stem cuttings

Table 2 shows the seedling quality and survival rates of the in vitrotissue-cultured plantlets according to the amount of sucrose andcoumarin added to the MS medium. As shown in Table 2, when the MS mediumwas supplemented with 80 g/L of sucrose and 0.025 mg/L of coumarin, thehighest seedling quality and survival rates were obtained.

TABLE 3 Hyponex (g/L) 0 1 2 3 Sucrose (g/L) 30 80 30 80 30 80 30 80Plant length 7.2 7.59 6.2 8.1 5.4 7.98 5.6 7.82 (cm/plant) Fresh weight0.53 1.03 0.61 1.19 0.56 1.08 0.57 1.01 (cm/plant) Survival rates 28 7969 83 55 80 57 77 of stem cuttings

Table 3 shows the seedling quality and survival rates of the in vitrotissue-cultured plantlets according to the amount of sucrose and hyponexadded to the MS medium. As shown in Table 3, the use of hyponex resultedin lower seedling quality and survival rates than when coumarin wasused.

The results of Test Examples 3 indicate that the basic mediumsupplemented with 80 g/L of sucrose and 0.025 mg/L of coumarin issuitable for producing high quality potato seedlings.

TEST EXAMPLE 4

This test was performed to establish an effective method for producingpotato seedlings according to the acclimatization of in vitrotissue-cultured plantlets. The pathogen-tested seedlings were allowed togrow for 30 days in a solid medium, which was prepared from a basic MSmedium at a pH of 5.8 supplemented with 9 g/L of agar and 30 g/L ofsucrose, and a liquid medium, which was prepared like the solid mediumbut excluding agar, in a culture room at 21° C. under 4,500 Lux lightingfor 18-20 hrs, and 0 Lux for 4-6 hrs using 4D fluorescent lamps.

In Group A, the in vitro plantlets were removed from culture bottles andimmediately planted through stem cutting without generalacclimatization. In contrast, Group B was subjected to anacclimatization process after being cultured in vitro. That is, the invitro plantlets were placed in a greenhouse having the same lightintensity and other conditions as in the culture room. The lightintensity in the greenhouse was gradually increased at time intervals oftwo to three days. Three to four days before being planted infacilities, aluminum foil was removed from culture bottles to allow thein vitro plantlets to adapt to atmospheric humidity. Then, the in vitroplantlets were removed from the culture bottles, and cut at node regionsat lower parts of stems using a disinfected sharp knife. Each test groupconsisted of 500 individuals, and a known potato cultivar “Superior” wasused in this test.

For perlite culture, three or four nodes containing growing points werecut from the in vitro-cultured disease-free seedlings with a disinfectedsharp knife, and directly planted in a sterile perlite-containing boxfor raising seedlings on a small scale. In an alternative method, theplantlets were planted in the perlite box in a way such that their rootsdeveloped upon in vitro culture. Sufficient 1:2 diluted MS solution wassupplied at time intervals of three days in order to prevent theplantlets from drying.

For deep culture, a culture bed of a deep flowing culture system wascompletely filled with a nutrient solution, and oxygen was supplied tothe nutrient culture using an air pump. For deep flow culture, anutrient solution supplied through a water outlet of a culture bedcontinuously flowed while contacting the roots of seedlings.

For DSCAC, a nutrient solution supplied to a culture bed was completelydrained and discharged through a helical discharge unit for water levelcontrol, which was placed below the nutrient solution, therebycompletely exposing the roots of potato seedlings in the dischargedculture bed to the air and enabling air influx and circulation throughholes for planting stem cuttings in an upper board of the culture bed.The nutrient solution was supplied for 30 min to the culture bed, andthe supply of the nutrient solution was interrupted for 90 min. Thesupply and interruption thereof of the nutrient solution werealternatively performed.

The results are given in Table 4, below.

TABLE 4 Deep Deep flow Perlite culture culture DSCAC Test group A B A BA B A B Death due to 127 103 132 106 102 97 84 99 desiccation/# ofplants Soft rot/# of 291 181 267 160 211 134 37 29 plants Acclimatized82 216 101 234 187 269 379 372 and survived individual number/# ofplants

As shown in Table 4, the in vitro-cultured seedlings cultivated in theDSCAC according to the present invention had the lowest death rates dueto desiccation, the lowest soft rot occurrence and the highest numbersof acclimatized and survived individuals. These results indicate thatthe DSCAC is the most effective method for acclimatizing invitro-culture plantlets.

TEST EXAMPLE 5

In order to investigate the occurrence of soft rot according to thedischarged state of the nutrient solution supplied to the root zone ofstem cuttings of in vitro-cultured potato seedlings, the invitro-cultured plantlets produced according to the same method as inTest Example 4 were tested under various conditions described in Table5, below.

TABLE 5 Nutrient solution level (discharged state) Nutrient ½ solutiondischarge 1/10 discharge circulation (below (remaining (supplied theroot in the Complete for 24 hrs) zone) bottom) discharge Soft rotoccurrence/ 500 455 189 41 plant Acclimatized and 0 5 311 459 survivedindividual number/plant

As shown in Table 5, good ventilation through complete discharge at theroot zone of potato seedlings planted through stem cutting preventssoftening of cut regions, as well as preventing root rot due toexcessive water supply.

TEST EXAMPLE 6

In order to determine a suitable time for supplying nutrient solution tothe potato seedlings planted through stem cutting, in vitro-cultureplantlets having a size of 6 cm, which were produced according to thesame method as in Test Example 4, were tested at an indoor temperatureof 21° C. and 4,500 Lux for 18-20 hrs, and 0 Lux for 4-6 hrs undervarious conditions described in Table 6, below.

TABLE 6 Nutrient solution supply interruption/supply 30 min/ 60 min/ 90min/ 120 min/ 160 min/ 180 min/ 210 min/ 30 min 30 min 30 min 30 min 30min 30 min 30 min Plant length 16.9 16.2 15.0 14.7 14.4 13.3 12.2(cm/plant) Damage due to 70 74 81 82 87 106 113 desiccation/# of plantsDamage due to 31 27 13 5 3 2 2 soft rot/# of plants

As shown in Table 6, the frequent supply of the nutrient solution wasbeneficial to the growth of potato seedlings, but caused soft rot due toexcessive water absorption. A long interruption of the nutrient solutionsupply caused wilting due to water evaporation from the plantlets,resulting in damage due to desiccation. When the nutrient solution wassupplied for 30 min, and this supply was then interrupted for 120 min,the amount of damage due to desiccation and soft rot decreased.

TEST EXAMPLES 7 AND 8

In order to investigate the effects of flow rates and circulation of anutrient solution supplied to a culture bed on the rooting of the potatoseedlings planted through stem cutting, in vitro-culture plantletshaving a size of 6 cm, which were produced according to the same methodas in Test Example 4, were planted through stem cutting in DSCACaccording to the present invention, and cultivated using a nutrientsolution, which was supplied for 30 min and interrupted for intervals of120 min, at an indoor temperature of 21° C. under 4,500 Lux lighting for18-20 hrs, and 0 Lux for 4-6 hrs. The radiation was performed two timesper day at 8:00 am and 8:00 pm.

TABLE 7 Straight-shaped Circular supply tube supply tube (0.5 × 5 cm)(2.5 cm diameter) Water pressure One- Three- One- Three- dispersion andnozzle nozzle nozzle nozzle supply tube (T) Rooting day/ 6.0 5.5 6.5 5.54.5 100 plants Root length on 0.5 1.1 0.7 1.0 1.8 about Day 10 afterplanting (cm/100 plants)

TABLE 8 Distance from supply tube for supplied nutrient solution (2.5 cmdiameter, 1 hp pump) Nutrient solution- 60 80 100 120 inflow point 20 cm40 cm cm cm cm cm First rooting 4.5 4.0 3.5 3.5 3.0 3.0 3.0 day/30plants Root length on 0.4 0.7 1.5 1.7 1.9 1.9 1.9 about Day 10 afterplanting (cm/100 plants)

As shown in Tables 7 and 8, the rapid flow rate and swirling due towater pressure generated by the supplied nutrient solution stress thepotato seedlings planted through stem cutting, thereby inhibiting thegrowth and rooting thereof.

TEST EXAMPLE 9

This test was performed to determine an effective method for shootgeneration through radiation, among the acclimatization conditions of invitro plantlets planted through stem cutting in DSCAC.

A known potato cultivar, “Superior”, was cultivated through in vitroculture in a solid medium, which was prepared with a basic MS mediumhaving a pH of 5.8 supplemented with 9 g/L of agar, 80 g/L of sucroseand 0.025 mg/L of coumarin, under 4,500 Lux lighting for 18-20 hrs, and0 Lux for 4-6 hrs. 500 individuals of the in vitro tissue-culturedSuperior were cut with a disinfected sharp knife to a length of about 6cm containing growing points. Cuttings were arranged in a randomizedcomplete block design with three replications. The cuttings were grownwith a nutrient solution, which was supplied for 30 min at aninterruption interval of 120 min, at room temperature of 21° C. underlight levels of 0 Lux, 2,100 Lux, 3,600 Lux and 5,500 Lux using 40Dfluorescent lamps. The length of potato seedlings was calculated bytaking the mean length of entire normally growing stem cuttings. Theinternode length was calculated by dividing the measured plant length bythe mean number of stem nodes.

TABLE 9 Radiation 0 Lux (dark condition) 2,100 Lux Treatment period(day) 0 1 2 3 4 0 1 2 3 4 Plant length (cm/plant) 6.3 6.7 9.4 11.9 13.16.0 6.1 6.7 7.8 9.3 Internode length (cm/plant) 0.8 0.9 1.2 1.5 2.0 0.80.8 0.9 1.0 1.2 Shoot generation (%) 0 38 82 100 100 0 13 35 59 75Damage due to soft/# of plants 0 0 0 3 77 0 0 0 5 9 Damage due todesiccation/# of plants 0 0 0 0 2 0 8 15 29 11 3,600 Lux 5,500 LuxTreatment period (day) 0 1 2 3 4 0 1 2 3 4 Plant length (cm/plant) 6.36.4 6.6 7.2 8.1 6.3 6.3 6.5 7.1 7.9 Internode length (cm/plant) 0.8 0.80.8 0.9 1.0 0.8 0.8 0.8 0.9 1.0 Shoot generation (%) 0 11 22 32 55 0 1023 34 59 Damage due to soft/# of plants 0 0 0 4 12 0 0 0 1 18 Damage dueto desiccation/# of plants 0 3 16 29 2 0 7 29 36 1

As shown in Table 9, compared to the acclimatization process of adaptingin vitro plantlets to the external environment in order to producepotato seedlings using the in vitro plantlets, which depends on theexperience and skill of growers, it was more cost-effective to placepotato seedlings planted through stem cuttings in dark conditions for aperiod of two to three days and then slowly harden the shoot sproutsgenerated at terminal and lateral buds of the planted stem cuttings touse the stem cuttings as potato seedlings.

TEST EXAMPLE 10

This test was performed in order to determine light levels and radiationtime suitable for the hardness of shoot sprouts generated after the invitro-cultured plantlets planted through stem cutting in DSCAC wereincubated under dark conditions.

The known potato cultivar “Superior” was cultivated through in vitroculture using a solid medium, which was prepared with a basic MS mediumof pH 5.8 supplemented with 9 g/L of agar and 80 g/L of sucrose, under4,500 Lux lighting for 18-20 hrs, and 0 Lux for 4-6 hrs. 500 individualsof the in vitro tissue-cultured Superior were cut with a disinfectedsharp knife to a length of about 6 cm containing growing points. Theplantlets were then planted and grown at room temperature, 21° C., usinga nutrient solution, which was supplied for 30 min and interrupted forintervals of 120 min. The light intensity was gradually increased usinga timer, and the light was radiated on the planted stem cuttings.

Table 10 shows the states of the in vitro-cultured plantlets grown for15 days after being planted through stem cutting. In Table 10, thecontrolled radiation time (day) is expressed, for example, as 3→1→1→1→9,which represents 3 days (the first step/0 Lux)→1 day (the secondstep/2,100 Lux)→1 day (the third step/3,600 Lux)→1 day (the fourthstep/5,500 Lux)→9 days (the fifth step/7,000 Lux).

TABLE 10 Controlled radiation time 3→1→1→1→9 3→2→2→2→6 3→3→3→3→33→2→1→1→8 Plant length (cm/plant) 10.4 13.1 16.1 12.8 Internode length1.1 1.1 1.5 1.1 (cm/plant) Node No./# of plants 9.6 12.3 10.8 11.7 Freshweight (g/plant) 0.27 0.28 0.29 0.29 Damage due to 62 19 4 13desiccation/# of plants Damage due to soft/# 6 12 58 18 of plants

As shown in Table 10, rapidly increased light levels acted as stressorson the sprouts from terminal and lateral buds generated from the invitro-cultured plantlets under the dark conditions, the sprouts havinglow adaptability to light. Radiation with suitable light levels on thegenerated sprouts may produce potato seedlings having stems with manyrobust and healthy nodes, which are required in hydroponics.

TEST EXAMPLE 11

This test was performed in order to establish automated controlledradiation according to the acclimatization of potato seedlings plantedthrough stem cutting and the hardening degree of stems based on theresults of Test Example 10. The potato seedlings were grown at roomtemperature of 21° C. using a nutrient solution, which was supplied for30 min at an interruption interval of 120 min.

TABLE 11 The quality of potato seedlings (grown for 30 days) PlantInternode Fresh Damage Automated control of length length weight Damagedue to due to radiation time (cm/plant) (cm/plant) (g/plant)desiccation/plant soft/plant Planting through stem 17.7 1.1 16.1 0 0cutting →60 h/0 Lux→ 50 h/2,100 Lux→ 40 h/3,600 Lux→ 30 h/5,500 Lux→ 540h/7,000 Lux

As apparent from the data of Table 11, when only disease-freetissue-cultured seedlings are selected and planted through stem cuttingby improving the unstable survivability of in vitro-cultured plantletsthrough rapid shoot generation and suitably increasing the lightintensity to the levels required for acclimatization, anyone may stablyproduce potato seedlings for use in planting in hydroponic facilities.

TEST EXAMPLE 12

This test was performed in order to investigate the collection amount ofpotato seedlings for cutting according to the growth of potato seedlingsplanted through stem cutting under automated controlled radiation. Thepotato seedlings were grown at room temperature, 21° C., using anutrient solution, which was supplied for 30 min at an interruptioninterval of 120 min.

TABLE 12 Collection day of cuttings of potato seedlings 10 13 16 19 2225 28 31 34 The amount of 0 42 126 408 34 311 65 312 77 collectedcuttings/ 5 cm in plant length

As shown in Table 12, the shoots (sprouts) having a size of 5 cm,generated from the terminal and lateral buds of the in vitro-culturedplantlets planted through stem cutting in DSCAC, could be collected 13days after planting stem cuttings. Also, the sprouts generated from stemcuttings could be collected every six days in a large amount.

TEST EXAMPLE 13

This test was performed in order to evaluate the seedling qualityaccording to planting through stem cutting of potato seedlings (5 cm to6 cm in plant length) for replanting, which were collected from DSCAC.

Each test group was cultivated under the following conditions. Forperlite culture, a volume of sterile perlite particles 3 cm to 5 cm indiameter was charged to a height of 7 cm into a rectangular plasticbasket 47 cm wide×37 cm long×9 cm high. Stem cuttings were planted atintervals of 2 cm while the lower two nodes were buried in the perlite.Nutrient solution was sufficiently supplied every two days in such a waythat it flowed on the bottom. For DSCAC, nutrient solution was suppliedfor 30 min, and the supply of the nutrient solution was interrupted for120 min. For SSCAC and the cultivation of potato seedlings planted inhydroponic facilities, nutrient solution was supplied for 30 sec, andthe supply of the nutrient solution was interrupted for 4 min. Duringperlite culture, DSCAC and SSCAC, the indoor temperature was maintainedat 21° C., and a light level of 7,000 Lux was maintained. Thecultivation of potato seedlings in hydroponic facilities was performedunder greenhouse conditions of the external environment.

TABLE 13 Planting Planting Planting through through through Direct stemcutting stem stem planting in in perlite cutting in cutting inhydroponic culture DSCAC SSCAC facilities Acclimatization of 100 100 100100 developed roots (%) Damage due to 0 0 0 0 wilting (%) Damage due tosoft 0 0 0 0 rot (%)

As shown in Table 13, potato seedlings for replanting through stemcutting, which were collected from DSCAC, had good quality, and thus hadhigh survival rates even when planted through stem cutting using anyculture method or when directly planted.

TEST EXAMPLE 14

This test was performed in order to determine whether the potatoseedlings for replanting through stem cutting according to the presentinvention are useful as potato seedlings for general field cultivation.Using in vitro-grown artificial seed potatoes (1-3 g) as a control,potato seedlings, which were rooted and hardened in the perlite cultureof Table 13 for 10 days and acclimatized for 5 days in a greenhouse,plug potato seedlings, which were obtained by planting through stemcutting potato seedlings for replanting through stem cutting in theDSCAC of Table 13 in bed soil in a plug tray, and hardening the plantedseedlings in a greenhouse for 15 days, and plug potato seedlings, whichwere produced by transplanting potato seedlings hardened in perliteculture for 10 days in bed soil in a plug tray, and growing the plantedseedlings in a greenhouse for 10 days were planted at intervals of 20 cmin two rows in PE mulching (total 1,200 seedlings/March 21), wherein2,000 kg of fully fermented compost, 10 kg of nitrogen, 10 kg ofphosphoric acid, 12 kg of potassium sulfate and 6 kg of insecticides(Mocap) against soil organisms were tilled into a 300 pyong (onepyong=3.3 m2) field. Seedlings were arranged in a randomized completeblock design with three replications. In order to prevent damage due todisease and harmful insects, 160 L of Form-D, 160 L of Mancozeb and 2 kgof Cornido were individually applied two times to the 300 pyong field.Potato harvest and evaluation were performed on June 25.

TABLE 14 Direct Plug seedlings from plug tray sowing of Seedlingsartificial Seedlings Seedlings planted in bed Seedlings seed produced inproduced in soil through through potatoes DSCAC perlite culute stemcutting transplanting Miss-planted 75% 37% 21% 8% 3% rates upon fieldplanting Plant length 40.2 cm 46.7 cm 63.0 cm 72.0 cm 89.1 cm Stolonnumber 4.8 11.4 10.1 11.5 11.4 Shoot tip length  0.6 cm  0.7 cm  0.7 cm 0.8 cm  0.8 cm Tuber 8.3  9.8  9.2 11.7 11.9 number/plant Tuber  191 g 278 g  311 g  339 g  372 g weight/plant

As shown in Table 14, the potato seedlings for replanting through stemcutting, which were produced in DSCAC, had good quality, and thus goodsurvival against the stresses of the external environment. Thus, whenpotato seedlings for direct cultivation in field are required, plugpotato seedlings produced using the plug tray are of good quality.

TEST EXAMPLE 15

This test was performed in order to investigate the effects of theleaves, remaining on the ground stems, on rooting when potato seedlingsproduced in DSCAC were replanted through stem cutting in SSCAC. Thereplanted seedlings were grown in a nutrient solution, which wassupplied for 30 min and interrupted for intervals of 120 min, at roomtemperature, that is, 21° C., under 7,000 Lux lighting for 18-20 hrs,and 0 Lux for 4-6 hrs. Light radiation was performed two times per dayat 9:00 am and 9:00 pm.

TABLE 15 Upper two Upper four Upper six Upper eight leaves leaves leavesleaves Rooting day after 4.5 4.5 4.5 4.0 replanting Damage due to 0 0 00 wilting (%) Damage due to soft 0 0 0 0 rot (%)

As shown in Table 15, the leaves remaining on the stems of potatoseedlings seldom affected rooting. However, it is preferable to performstem descending work after all of the leaves except for upper two orthree leaves are removed in order to produce seedlings having long stemswith many nodes, which are required in hydroponics.

TEST EXAMPLE 16

This test was performed using seedlings grown to 10 cm in order toinvestigate the effects of the length of roots removed from seedlings onrooting upon stem descending of potato seedlings in SSCAC. The seedlingswere grown at an indoor temperature of 21° C. under 7,000 Lux lightingfor 18-20 hrs, and 0 Lux for 4-6 hrs. A nutrient solution sprayed ontopotato seedlings was supplied for 30 sec, and the supply of the nutrientsolution was interrupted for 4 min. The supply and interruption of thenutrient solution were alternately repeated. The roots were consideredto be regenerated when they had five or more root hairs and were 0.5 cmor longer.

TABLE 16 The degree of root cut of potato seedlings Complete No cut ½cut ¾ cut removal Wilting day of leaves and stems 6 4 3 6 upon plantingRoot regeneration day 6.0 4.0 4.0 4.5 Plant length after 10 days 12.915.1 16.8 14.5

As shown in Table 16, the best results were obtained when three quartersof the roots of potato seedlings to be replanted through stem cuttingwere cut, and the potato seedlings having only one quarter of the rootswere subjected to stem descending work.

TEST EXAMPLE 17

This test was performed in order to compare the quality of potatoseedlings produced according to the methods described in Table 17. 2,000potato seedlings were planted and cultivated in hydroponics having anapparatus and a control method for maintaining the environment of rootzone at optimal levels.

TABLE 17 Tissue- Tank- cultured cultured Seedling DSCAC SSCAC seedlings/seedlings/ sprouts/ seedlings/ seedlings/ 7 cm 8 cm 7 cm 8 cm 35 cm Daysuntil  6  6  3  4  3 rooting begins Damaged 63% 49% 0% 16% 0% seedlingsupon planting in hydroponics Primary  8  8 7 11 14 stolon number Daysuntil 42 38 33 39 37 reproductive growth phase Number of 24 29 27 33 41plants over 5 g

As shown in Table 17, potato seedlings produced in DSCAC and SSCAC werefound to have the best quality.

TEST EXAMPLE 18

This test was performed in order to establish a method for producingpotato seedlings suitable for planting and capable of undergoing rapidrooting when planted in hydroponic facilities. After all of the leavesexcept for the uppermost three leaves had been removed from potatoseedlings grown 30 cm or longer that had undergone the SSCA step ofExample 1, the potato seedlings were planted in facilities in which theroot zone environment was automatically controlled with respect to theday length and temperature.

TABLE 18 States of root zone of potato seedlings planted in hydroponics¾ cut Seedlings Seedlings Seedlings Seedlings seedling acclimatizedacclimatized acclimatized acclimatized on for 3 days for 5 days for 7days for 9 days planting after ¾ after ¾ after ¾ after ¾ day cuttingcutting cutting cutting Wilting day of leaves and 3 2 0 1 5 stems uponplanting After Plant length 16.8 cm 17.1 cm 18.3 cm 17.9 cm 15.2 cm 10days Root length  0.6 cm  0.9 cm  7.7 cm  8.4 cm  0.5 cm

As shown in Table 18, when seedlings produced in SSCAC were acclimatizedfor 5 days to 7 days after all of the leaves except for the uppermostthree leaves had been removed prior to planting in hydroponicfacilities, they underwent better initial growth, leading to highrooting rates.

INDUSTRIAL APPLICABILITY

As described hereinbefore, according to the present invention, when invitro-cultured plantlets are planted in DSCAC through stem cutting, andsprouts from the terminal and lateral buds of the plantlets are hardenedby gradually increasing light levels from the dark condition, theplantlets have healthy dark-green leaves and a high accumulation ofcarbohydrates, thereby giving rise to potato seedlings having long stemsand stems which appear robust and are not overgrown, and elastic andshort nodes. When planted in hydroponic facilities, such potatoseedlings have high adaptability to the external environment and thusrapidly uniformly generate roots in a short time. The rapid rootanchoring prevents planted seedlings from withering, leading to death,growing poorly, and the like.

The direct planting of in vitro plantlets through stem cutting without aseparate acclimatization process shortens the overall time required toproduce potato seedlings by omitting the acclimatization process.

The DSCA according to the present invention comprises supplying anutrient solution and interrupting the supply of the nutrient solution.While the supply of the nutrient solution is interrupted, the nutrientsolution and growth debris are completely discharged, and thecirculating nutrient solution is filtered through a sieving net and thensupplied again, thereby preventing soft rot and rot diseases in theroots in the root zone and stems.

In addition, disease-free potato seedlings can be repeatedly collectedin the DSCA, making it possible to mass produce disease-free potatoseedlings. Thus, the present invention is more cost-effective and lesslabor-intensive.

Further, the present invention enables the production of robust potatoseedlings having many round nodes capable of maximizing the number ofstolon and achieving a plant length of 30-40 cm by further subjectingthe potato seedlings, having undergone thedeep-flow-stem-cutting-and-acclimatization process, to the SSCA step.

1. An apparatus for generating seedling of seed potato comprising: aculture panel, in which holes for planting of stem cuttings arearranged, to plant potato seedlings through stem cutting and cultivatethe seedlings; a culture bed, which has a space in which the culturepanel is placed, contains a supplied nutrient solution required for thegrowth of the potato seedlings planted through stem cutting in theculture panel, and has a water outlet for discharging the excessivelysupplied nutrient solution; a light source, which is provided at the topof the culture bed and radiates light on potato seedlings plantedthrough stem cutting in the culture panel; a nutrient solutiondispersion and supply tube which is provided at one side of the culturebed and flows and supplies the nutrient solution to the culture bed; anda nutrient solution preparation and supply part which comprises anutrient solution tank and a nutrient solution supply pump provided inthe nutrient solution tank, wherein the nutrient solution tank isconnected to the nutrient solution dispersion and supply tube andsupplies the nutrient solution thereto by the operation of the nutrientsolution supply pump, wherein the water outlet of the culture bed isprovided with a water discharge tube having a slit in a longitudinaldirection, and an opening and closing tube having a helical opening andclosing part is inserted into the water discharge tube in a separatedstate against a lower part of the water discharge tube.
 2. The apparatusaccording to claim 1, wherein the culture bed is formed in two layers bya support frame in which the space in which the nutrient solution isheld is formed in two layers, the nutrient solution dispersion andsupply tube connected to the nutrient solution tank is placed in thespace formed at each layer of the support frame, and fluorescent lampsas the light source are arranged in two rows at a lower part of theculture bed formed at each layer of the support frame.
 3. The apparatusaccording to claim 2, wherein a main supply tube is placed in one sideof the support frame and is connected to the nutrient solutiondispersion and supply tube at each layer to supply the nutrientsolution, the main supply tube has a flow control valve between thenutrient solution dispersion and supply tubes, to control an inflowingamount of the nutrient solution, the main supply tube is placed in anupright orientation such that it extends to an upper part of the culturebed placed at the uppermost part of the support frame, the uppermostpart of the main supply tube is greater in volume than a lower part, andis coupled with a pressure tube connected to the nutrient solution tank,and a pressure control valve for controlling the pressure against themain supply tube is placed between the main supply tube and the pressuretube.
 4. The apparatus according to claim 1, wherein the water outlet ofthe culture bed includes a discharge tube which is connected to thenutrient solution tank and recovers the discharged nutrient solutioninto the nutrient solution tank.
 5. The apparatus according to claim 4,wherein a micro-sieving net is placed at a terminal part of thedischarge tube to sift sediments or impurities contained in thecirculating nutrient solution.
 6. The apparatus according to claim 1,wherein one side of the nutrient solution dispersion and supply tube isa T-shaped branch tube into which the nutrient solution is supplied fromthe nutrient solution tank, and the branch tube has an effusion tube inwhich a nozzle from which the nutrient solution flows out is formed, andwhich is horizontally provided at a lower surface of the culture bed. 7.A system for generating seedling of seed potato, wherein the systemcomprises: a first apparatus according to claim 1 and, a secondapparatus comprising: a culture panel in which holes for planting stemcuttings are formed to plant potato seedlings through stem cutting andcultivate them; a culture bed in an upper part of which the culturepanel is supported and which has a spray tube having nozzles spraying ina mist form a nutrient solution required for the growth of the potatoseedlings planted through stem cutting in the culture panel, and a wateroutlet for discharging the nutrient solution that has been sprayed andhas flowed down; a main supply tube which is connected with the spraytube and flows the nutrient solution to the culture bed; a light sourcewhich is provided at the top of the culture bed and radiates light onpotato seedlings planted through stem cutting in the culture panel; anda nutrient solution preparation and supply part which comprises anutrient solution tank and a nutrient solution supply pump provided inthe nutrient solution tank, wherein the nutrient solution tank isconnected to the main supply tube and stores the nutrient solution, andthe nutrient solution is supplied with the spray tube through the mainsupply tube by the operation of the nutrient solution supply pump.